Alkoxylated unsaturated carboxylic acid additives for low-sulfur fuels

ABSTRACT

Compositions comprising: (i) a fuel component selected from the group consisting of diesel, gasoline, kerosene, other hydrocarbons which are liquid at room temperature and mixtures thereof; and (ii) and an additive of the general formula (I) are described:
 
R—COO—(C n H 2n —O) k —H  (I)
wherein R represents a mono- or poly-unsaturated alkylene group having from 10 to 17 carbon atoms, n is 2 or 3, and k represents a number of from 0.5 to 3; wherein the fuel component is present in an amount of more than 50% by weight, wherein the additive is present in an amount of from 0.001 to 0.1% by weight; and wherein the composition has a sulfur content of 0.2% by weight or less, all weight percents based on the composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/495,802,filed May 17, 2004, which is a national stage entry of InternationalApplication No. PCT/EP02112371, filed on Nov. 6, 2002 which designatedthe United States of America and which claims priority of German PatentApplication number DE 10156024.9, filed Nov. 15, 2001, the entirecontents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Fuels based on petroleum or petroleum derivatives generally containsmall amounts of sulfur. Crude oils normally contain between 2 and 0.5%by weight of sulfur. In the combustion of these sulfur-containing fuels,sulfur dioxide is formed as a combustion product and is oxidized in airto sulfuric acid which can cause serious environmental damage in theform of acid rain. Accordingly, there has long been a demand to reducethe sulfur content in petroleum products, more particularly in fuels.However, not only does sulfur have adverse effects, it also serves inthe small quantities in which it is normally present as a lubricantimprover which is entirely desirable in many technical applications, forexample as a fuel for combustion engines. Accordingly, the use oflow-sulfur fuels often leads to problems to do with the friction of thecorrespondingly fuelled machine parts. In order to meet environmentaland emission control requirements on the one hand and frictioncoefficient requirements on the other hand, additives are normallyincorporated in the fuels. It is known from WO 94/17160 that esters ofcarboxylic acids and alcohols containing more than 1 carbon atom areadded to low-sulfur fuels, preferably diesel fuels, to adjust thecorresponding friction coefficients. Esters of C₂₋₅₀ carboxylic acidsand polyols are preferably used. However, the problem arises that, withsmall additions of expensive additives, the lubricating effect of thefuels thus obtained is not always satisfactory. Accordingly, the problemaddressed by the present invention was to provide an additive forlow-sulfur fuels which, even in small amounts, would enable thelubricating effect of fuels to be adequately improved.

BRIEF SUMMARY OF THE INVENTION

The present invention relates, in general, to low-sulfur fuelcompositions which contain certain alkoxylated esters as additives.

Accordingly, the present invention relates to fuel compositionscontaining more than 50% by weight of diesel, gasoline, kerosene orother hydrocarbons liquid at room temperature, these fuel compositionscontaining an additive corresponding to formula (I):R—COO—(C_(n)H_(2n)—O)_(k)—H  (I)where R is a mono- or polyunsaturated alkylene group containing 10 to 17carbon atoms and n=2 or 3 and k is a number of 0.5 to 3, in quantitiesof 0.001 to 0.1% by weight, with the proviso that the fuel compositionhas a sulfur content of at most 0.2% by weight.

The fuel compositions according to the invention are furtherdistinguished by the fact that the sulfur content is at most 0.2% byweight, based on the fuel composition.

DETAILED DESCRIPTION OF THE INVENTION

Fuels in the context of the present invention are understood to be anyenergy-yielding working materials of which the free combustion energy isconverted into mechanical work. Such materials include all types ofmotor and aircraft fuels which are liquid at room temperature and normalpressure. Motor fuels, for example for automobile and truck engines,generally contain hydrocarbons, for example gasoline or higher-boilingpetroleum fractions.

Diesel fuels are low-inflammability mixtures of liquid hydrocarbonswhich are used as fuels for constant-pressure or compression-ignitionengines (diesel engines) and which consist predominantly of paraffinswith impurities in the form of olefins, naphthenes and aromatichydrocarbons. Their composition is variable and depends in particularupon the production method. Diesel is obtained, for example, from gasoil by cracking or from tars obtained in the low-temperaturecarbonization of brown coal or hard coal. Typical products havedensities of 0.83 to 0.88 g/cm³, boiling points in the range from 170 to360° C. and flash points of 70 to 100° C. Diesel oils for stationaryplant and for marine engines are similar in composition to heavy fueloil while those for automobiles, buses and trucks correspond to fueloil.

During combustion in a diesel engine, air is taken into the cylinder,heated to 550-900° C. by high compression (compression ratio 14:1 to25:1), so that a jet of diesel injected in ignites spontaneously andreaches a combustion pressure of 50-80 bar at a combustion temperatureof 1500-2200° C. so that the piston is moved and work is done. 13 m³ airare used in the combustion of 1 liter of diesel in the diesel engine.The combustion energy released amounts to ca. 42,000 kJ/kg.

A key factor for the usability of diesel fuels is their ignitionresponse which is quantitatively expressed by the cetane number.Ignition response is the capacity of a motor fuel to ignite relativelyeasily or with relative difficulty in an engine operating on the dieselprinciple. With every fuel, this requires not only atomization, pressureand temperature, but also a conditioning interval (ignition delay)before discernible combustion. Good ignition response of a fuel meansfavorable starting behavior and quiet running of the diesel engine byvirtue of a short conditioning interval or small ignition delay. With alarge ignition delay, the known phenomenon of “knocking” comes audiblyinto play. The requirements for diesel fuels are a cetane number of 20to 40 for slow-running engines and a cetane number of >45 for small andfast-running engines. Other desirable properties include a low pourpoint, a low content of incombustible or soot-forming substances and alow sulfur content.

The fuel compositions according to the invention contain diesel,gasoline, kerosene or other hydrocarbons liquid at room temperature, forexample hexane or pentane. Fuel compositions containing diesel as fuelare particularly preferred. In principle, the fuel compositionsaccording to the invention may also contain mixtures of, for example,gasoline and kerosene in any ratio.

The additives of formula (I) are alkoxylated carboxylic acid estersknown per se. It is one of the key aspects of the present invention thatthe carboxylic acids must be unsaturated carboxylic acids containing 11to 17 carbon atoms in the alkyl chain. Compounds of formula (I), inwhich R is an unsaturated group containing 17 carbon atoms, areparticularly preferred. Oleic acid is particularly preferred for thepurposes of the invention. The alkoxylation, i.e. the reaction of theacid with ethylene oxide and/or propylene oxide, is carried out in knownmanner, cf. for example U.S. Pat. No. 5,326,891 or U.S. Pat. No.5,292,910 which describe the synthesis of such compounds where the acidsare reacted with the alkoxides in the presence of selected hydrotalcitecatalysts to form the required alkoxylated compounds. Also of relevancein this regard is the disclosure of WO 98/25878 which describes aprocess for the synthesis of these “short-ethoxylated” fatty acids byreaction of the fatty acids in the presence of alkanolamines.

One feature of the present additives of formula (I) is that the numberof alkoxide units per molecule is strictly limited and is preferably 1,i.e. 1 part acid and 1 part alkoxide have reacted. Since, in addition,the use of modern catalysts does not provide for uniform products,mixtures of different alkoxylated compounds are usually present which isexpressed in the partly broken number k in formula (I). Compounds offormula (I) where n=2, i.e. ethoxylated fatty acids, are particularlypreferred. The index k should preferably have a value of 0.5 to 1.5,compounds of formula (I) where k=1 being most particularly preferred.Compounds of formula (I) where k=1 and n=2 are also preferred. The fuelcompositions according to the invention contain the additives of formula(I) in quantities of preferably 0.001 to 0.01% by weight and morepreferably 0.001 to 0.005% by weight. Oleic acid esters containing 1part ethylene oxide are particularly preferred.

In a particularly preferred embodiment, the additives of formula (I)according to the invention are used in fuel compositions with anextremely low sulfur content, i.e. a sulfur content of 0.005 to at most0.05% by weight. In a most particularly preferred embodiment, they areused in fuel compositions with a sulfur content below 0.005% by weight.The aromatics content of the claimed fuel compositions should be below25% by volume and is preferably below 20% by volume. Fuel compositionscontaining less than 5% by volume of aromatics are particularlypreferred, fuel compositions free from aromatics being most particularlypreferred.

If diesel is selected as the actual fuel, it should have a cetane numberbelow 50 and preferably below 45. The cetane number of the diesel shouldbe below 50.

The addition of the compounds of formula (I) leads to a good broadeffect of the corresponding fuels, the HFRR value at 60° C. being 600μm, preferably at most 500 μm and more particularly 400 μm or less. TheHFFR (high-frequency reciprocating rig) value is used to measure thefriction of fuels in use. A detailed description of this method can befound in ISO/TC22/SC7/WG6/N188.

The fuels according to the invention may contain other typicaladditives, for example cetane number improvers (saltpeter or nitrousester), corrosion inhibitors, flow enhancers, surfactants (which keepthe fuel injectors clean), defoamers and smoke reducers.

In choosing the additives for the fuel compositions according to theinvention, it is important to bear in mind that the use of, for example,fatty alcohols and/or alkoxylated fatty alcohols and/or alkanolamidesand/or derivatives thereof is preferably ruled out. Fuel compositionswhich contain only the additives of formula (I) for reducing frictionare most particularly preferred.

The use of the above-defined compounds of formula (I) in fuels, moreparticularly in diesel fuels, leads on the one hand to satisfactorylubrication behavior of the fuels without any of the adverse ecologicalconsequences typical of low-sulfur fuels. In addition, the fuelscontaining the additives according to the invention show excellentlow-temperature behavior with no flocculation, even at low temperatures.

EXAMPLES

An oleic acid ester containing 1 mol ethylene oxide per mol fatty acidwas tested for its effectiveness in reducing the friction coefficient ofdiesel (HFRR) by comparison with a commercially available glycerolmono-oleic acid ester (GMO). The additive was used in a quantity of 50ppm. Additive-free diesel was used as the reference fuel.

The HFRR value of the additive-free diesel was 591 μm. A value of 529 μmwas measured for the GMO-containing diesel whereas the additiveaccording to the invention achieved an HFRR value of 500 μm.

1-16. (canceled)
 17. A composition comprising: (i) a fuel componentselected from the group consisting of diesel, gasoline, kerosene, otherhydrocarbons which are liquid at room temperature and mixtures thereof;and (ii) and an additive of the general formula (I):R—COO—(C_(n)H_(2n)—O)_(k)—H  (I) wherein R represents a mono- orpoly-unsaturated alkylene group having from 10 to 17 carbon atoms, n is2 or 3, and k represents a number of from 0.5 to 3; wherein the fuelcomponent is present in an amount of more than 50% by weight, whereinthe additive is present in an amount of from 0.001 to 0.1% by weight;and wherein the composition has a sulfur content of 0.2% by weight orless, all weight percents based on the composition.
 18. The compositionaccording to claim 17, wherein n is
 2. 19. The composition according toclaim 17, wherein k represents a number of from 0.5 to 1.5.
 20. Thecomposition according to claim 17, wherein k is
 1. 21. The compositionaccording to claim 18, wherein k represents a number of from 0.5 to 1.5.22. The composition according to claim 18, wherein k is
 1. 23. Thecomposition according to claim 17, wherein R represents a mono- orpoly-unsaturated alkylene group having 17 carbon atoms.
 24. Thecomposition according to claim 17, wherein R represents amono-unsaturated alkylene group having 17 carbon atoms.
 25. Thecomposition according to claim 21, wherein R represents a mono- orpoly-unsaturated alkylene group having 17 carbon atoms.
 26. Thecomposition according to claim 21, wherein R represents amono-unsaturated alkylene group having 17 carbon atoms.
 27. Thecomposition according to claim 17, wherein the additive is present in anamount of from 0.001 to 0.01% by weight.
 28. The composition accordingto claim 23, wherein the additive is present in an amount of from 0.001to 0.01% by weight.
 29. The composition according to claim 25, whereinthe additive is present in an amount of from 0.001 to 0.01% by weight.30. The composition according to claim 17, wherein the composition has asulfur content of from 0.005 to 0.05% by weight.
 31. The compositionaccording to claim 17, wherein the composition has a sulfur content of0.005% by weight or less.
 32. The composition according to claim 17,wherein the composition has an aromatic content of less than 25% byvolume.
 33. The composition according to claim 17, wherein the fuelcomponent comprises a diesel having a cetane number below
 50. 34. Thecomposition according to claim 17, wherein the composition has an HFRRfriction coefficient at 60° C. of at most 500 μm.
 35. The compositionaccording to claim 17, wherein the composition is free of fattyalcohols, alkoxylated fatty alcohols and alkanolamides.